The present invention relates generally to tiled emissive displays, which include a plurality of tiles, which are aligned to produce an image.
Flat panel technology has been dominated by liquid crystal displays (LCD""s) in which the liquid crystal material acts as a valve to transmit light from a back light source. Large displays are usually smaller displays tiled together. For large LCD panels the tile building blocks are generally complete displays with the liquid crystal material in the cavity defined by two glass plates that are sealed around the perimeter. The edges of the sealed tiles are cut and polished to minimize the distance from the edge pixel to the edge of the tile. The integrity of the seal around the LCD material must be maintained thereby limiting the amount of cutting and polishing that is possible. Furthermore, variability in the performance from one tile to another can create discontinuities in the large panel image. The tiles are usually tested and sorted to minimize tile variability.
U.S. Pat. No. 5,980,348 describes a method for aligning and attaching LCD tiles for large panel displays. A mechanical alignment system is employed. U.S. Pat. No. 5,903,328 describes tiled LCD displays where the adjacent tile edges are ground at an angle and overlap each other. This allows a small increase in the space for the ground edge relative to the adjacent pixels; however, as the space increases the distance between the image planes of adjacent tiles increases proportionally. U.S. Pat. No. 5,889,568 describes a tiled LCD display wherein masking techniques are used to hide the seams between tiles. The mask can be positioned behind of the LCD tile to block stray light from the back light as well as in front of the tile. U.S. Pat. No. 5,781,258 describes an LCD tiled display wherein the half tiles are used and the final filling of the LCD material is completed within the cavity of all the tiles simultaneously.
Emissive displays, which produce their own light, have a very different structure from LCDs. The emissive material is deposited on to the substrate surface. A back plate or thin film coating provides protection from the environment. The organic and polymeric materials that produce light are sensitive to environment, heat and dirt. The preparation of the edges of emissive tiles is difficult due to the potential exposure to contaminants.
It is an object of the present invention to provide a large flat panel tiled emissive display with continuity of the pixels, both in light-emitting characteristics and in spacing, across the display area.
This object is achieved by a method of making a tiled emissive display having at least two aligned tiles, comprising the steps of:
a) finishing at least one edge of each tile and aligning the finished edges of such tiles;
b) forming a monolithic structure including aligned tiles, each such aligned tile having a substrate, TFT circuits, drive circuits and bottom pixel electrodes for providing electrical signals to pixels in the corresponding tile;
c) coating the aligned tiles with material that produces light when activated by an electric field; and
d) forming at least one top pixel electrode over the coated material so that the coated material produces light when activated by an electric field from the electrode.
It is an advantage of the present invention that individual tiles can be prepared, aligned and joined together prior to the deposition of light emitting materials. The aligned tiles are processed as a monolithic structure. By coating the joined tiles as a single flat panel, the process of polishing, squaring and aligning the edges of the tiles is complete prior to deposition. The preparation of the edges of the tiles produces many particles and is serious source of contamination; in the present invention, the debris from these operations can be removed prior to deposition of organic materials. The monolithic structure can be cleaned and the light-emitting materials are then deposited in a clean environment without further need to prepare the edges or handle the tiles for alignment.
It is a further advantage of the present invention that all the tiles in a single display are coated concurrently. Typically, for tiling of active matrix LCD displays, the tiles are sorted and characterized and then tiled together. However, any variations are readily evident at the seams. By coating all the tiles concurrently, the variations from different process runs and material lots are eliminated. Therefore, the tile-to-tile characteristics are indistinguishable across the seam.
It is a further advantage of the present invention that by coating the tiles as a monolithic structure the coating can be continuous across tiles thereby reducing coating edge effects within the tiled array. By eliminating the edge effects, active pixels can be placed along the edge of the tiles to allow for pixel pitch integrity from tile to tile.
It is a further advantage of the present invention that the coated monolithic structure can be immediately packaged and encapsulated in its entirety. The monolithic structure is therefore more readily protected from the environment. Individual tiles do not need to be handled after deposition of the sensitive light emitting materials; elimination of this handling time greatly reduces risk of environmental degradation and increases yield and reliability of the display.
It is a further advantage of the present invention that higher temperature joining techniques can be used to bond tiles to make the monolithic structure. By bonding the tiles prior to deposition of the light emitting materials high temperature processes including metal bonding, high temperature adhesive, microwave bonding, and fusion joining can be used. In addition, ultraviolet light activated adhesives can be used prior to deposition of light emitting material.
It is a further advantage of the present invention that electrical interconnections to the monolithic structure can be established prior to coating deposition. Connection techniques that require high temperature, ultrasonics or pressure can be used only when the light emitting materials are not present. By positioning the tiles prior to deposition of the light emitting material, electrical connections can be made to a back plate by means including soldering, ultrasonic bonding, microwave bonding, and conductive adhesives. Furthermore, electrical escapes including attachment of flex connections at high temperatures including soldering, can be established. Cleaning of the monolithic structure after electrical connections are made and prior to deposition of the light emitting materials facilitates high quality displays.
It is a further advantage of the present invention that it is suitable for use in organic electroluminescent displays. A feature of the invention is that it can be readily manufactured and the display will not produce artifacts caused by aligned tiles.
It is advantageous to prepare the tile edges and align the tiles prior to deposition of the light emitting materials.